1. Field of the Invention
The present invention relates to a plunger seal for a pump which is used as a reciprocating seal of a high-pressure fuel pump in a fuel injection pump for a direct-injection gasoline engine, and used for all other oil pressure, air pressure and water pressure equipments.
2. Description of the Conventional Art
The direct-injection gasoline engine is structured such as to directly inject a high-pressure fuel into a cylinder so as to burn for the purpose of a regulation of exhaust gas, an improvement of specific fuel consumption and the like in recent years. Since a high pressure performance is demanded in the fuel injection pump used for directly injecting the high-pressure fuel, a performance standing against a high pressure is demanded in a plunger seal for the pump used in the fuel injection pump.
Conventionally, as the plunger seal for the pump used in the fuel injection pump, there has been known a rubber lip type seal member integrally having a fuel seal lip sealing the fuel such as the gasoline or the like at high pressure in a sealed object side, and an oil seal lip sealing an oil existing in an opposite side to the sealed object for cooling and lubricating (refer to Japanese Unexamined Patent Publication No. 8-68370). However, since a material of the seal lip is constituted by the rubber, there is a problem that a sealing function can not be sufficiently satisfied with respect to a lack of pressure tightness due to the high pressure and a lack of fuel resistance accompanied by an increase of an alcoholic content in the fuel.
Accordingly, there has been proposed a structure in which the fuel seal lip is made of the resin and is independently provided from the rubber oil seal lip, whereby it is possible to maintain the pressure resistance even if the pressure of the high-pressure fuel becomes higher, and it is possible to prevent a swelling and a reduction of hardness and strength with respect to the alcohol contained fuel or the like (refer to the patent document WO 02/099320A1). However, since the fuel seal lip and the oil seal lip are independently provided, an installation space is increased, so that there is a problem that it is impossible to respond to a demand for a compact structure, and it is impossible to secure a stable seal performance with respect to a higher performance requirement of the fuel pump. Further, since a demand for a low cost is increased, it is necessary to respond to this. It is necessary to reduce a number of seals for reducing an assembling man-hour.
Further, there has been known that, when a metal spring having an approximately U-shaped cross section and applying an energizing force in a diametrical direction is installed in a groove formed in the rubber fuel seal lip, a fixing collar for preventing the metal spring from jumping out is provided in an opening portion of the groove (refer to Japanese Patent No. 2651407). However, if the fixing collar is provided in the case that the fuel seal lip is constituted by the resin material, a shape thereof becomes complicated, it is hard to manufacture the seal lip of the resin material by a normally used injection molding machine. Accordingly, there has been proposed that an inner surface of the grove is formed flat while abolishing the fixing collar, in the case that the resin fuel seal lip in which the metal spring having the approximately U-shaped cross section is installed is manufactured by the injection molding machine (refer to Japanese Patent No. 2955822).
Further, as shown in FIG. 16, in the conventional fuel seal lip 101 using the rubber material, a shape of the seal lip 101 is specified by setting angles α and β formed by both side surfaces 103 and 104 of the seal lip 101 with respect to a plunger 102 at a time of installing the plunger 102, and a surface pressure gradient P generated in a contact surface of the seal lip 101 at a time of installing the plunger 102 is controlled as shown in FIG. 17, whereby it is possible to control a thickness t of a seal medium interposed between the seal lip 101 and the plunger 102 so as to secure a sealing performance (a leak amount) in accordance with a set seal performance. However, if the material of the fuel seal lip 101 is changed to the resin such as PTFE or the like, the angle α and β corresponding to the shape of the seal lip 101 are deformed and changed by use on the basis of a creep characteristic. Accordingly, the surface pressure gradient P generated in the contact surface of the seal lip 101 is changed, and it is hard to secure the seal performance (the leak amount) in accordance with the set value.